While I don't generally advocate attempting to have a sane discussion with this type of person, in light of the idiocy of his comments re no soul so it's a waste to do rescue (one has nothing to do with the other) why not ask him what his particular religion dictates about kindness and compassion. Every living creature deserves that while they are alive, whether they have a soul or not. Can he really say that he advocate's cruelty and suffering as the alternative?
But if you would rather not get into with him then you are probably just going to have to ignore his stupdity as hard as that may be.
But if you would rather not get into with him then you are probably just going to have to ignore his stupdity as hard as that may be.